The present invention relates to an ink liquid supply system for an ink jet system printer and, more particularly, to an ink liquid viscosity control system for maintaining the ink liquid viscosity within a preselected range.
An ink jet system printer of the charge amplitude controlling type has been widely used in, for example, a word processor, a facsimile printer and a computer output device. The ink jet system printer of the charge amplitude controlling type ensures a clean printing in a rapid and quiet operation.
In such an ink jet system printer, an ink liquid of a predetermined pressure is supplied to a nozzle to emit ink droplets at a preselected frequency. Ink droplets not contributing to the actual printing operation are directed to a beam gutter for recirculation purposes. Therefore, the ink liquid viscosity gradually increases while the printer operates because the volatile component included in the ink liquid volatilizes during time period when the ink droplets travel from the nozzle to the beam gutter through the air. On the other hand, it is strictly required that the ink liquid viscosity be maintained within a preselected range to ensure an accurate droplet formation.
A viscosity detection system is required if the system is desired to be constructed to control the ink liquid viscosity. Conventional viscosity detection systems of the laboratory type such as a rotation viscosimeter and an ultrasonic viscosimeter are expensive and occupy a large space. Thus, the conventional viscosity detection systems are not suited for detecting the ink liquid viscosity in an ink liquid supply system for an ink jet system printer. Further, the above-mentioned conventional viscosity detection systems must be placed in a constant temperature environment.
On the other hand, an ink liquid viscosity control system in an ink liquid supply system is disclosed in U.S. Pat. No. 4,190,846, INK LIQUID CONCENTRATION CONTROL IN AN INK LIQUID SUPPLY SYSTEM FOR AN INK JET SYSTEM PRINTER, issued on Feb. 26, 1980. In this system, a semipermeable membrane is employed to control the ink liquid concentration. Such a control system can not ensure a long period of operation due to the semipermeable membrane.
Accordingly, an object of the present invention is to provide an ink liquid viscosity control system in an ink liquid supply system for an ink jet system printer.
Another object of the present invention is to provide an ink liquid supply system for an ink jet system printer, which ensures an accurate operation of the printer.
Still another object of the present invention is to provide a small size ink liquid viscosity control device which ensures an accurate viscosity control.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, an ink liquid viscosity detection unit is incorporated in a sub tank included in the ink liquid supply system for an ink jet system printer. The ink liquid viscosity detection unit includes a float element disposed in the ink liquid contained in the sub tank, the float element has a specific gravity slightly greater than the spcific gravity of an ink liquid of a preferred viscosity. When the ink liquid viscosity becomes large and the specific gravity of the ink liquid becomes greater than that of the float element, the float element moves upward. The upward movement of the float element is detected by a detection unit which develops a control signal to add a dilution to the ink liquid contained in the sub tank, thereby maintaining the ink liquid viscosity within a predetermined range.